Japan suffers an estimated annual economic loss of around ¥1 trillion due to the “social jet lag” mismatch between sleep patterns on weekdays and holidays, according to a recent study.

The estimate comes from a University of Tsukuba research group that analyzed data from about 80,000 workers who use a sleep app on their smartphones.

According to the researchers, this is the first large-scale study to examine the relationship between sleep patterns and labor productivity. “Not only sleep duration but also sleep quality and irregular sleep schedules were found to be strongly associated with declines in labor productivity,” the group said.

The research group, led by professor Masashi Yanagisawa, director of the International Institute for Integrative Sleep Medicine at the University of Tsukuba, analyzed about 2.1 million nights of sleep data from roughly 80,000 working adults in Japan. All participants were users of the Pokemon Sleep app and provided informed consent.

The researchers examined the relationships between five indicators — including total sleep time and chronotype, such as morning type and night type — and participants’ self-rated work performance over the previous four weeks.

They found that productivity fell when sleep duration was either too short or too long. The study also showed that difficulty falling asleep, waking during the night, and large differences between weekday and weekend sleep duration were all associated with poorer job performance.

Using artificial intelligence, the researchers classified sleep patterns into five types: healthy sleep, long sleep, fragmented sleep, poor-quality sleep and social jet lag. Among them, poor-quality sleep and social jet lag were linked to especially large declines in productivity.

Social jet lag occurs when there is a consistent mismatch between weekday and holiday bedtimes and wake-up times, creating a “time lag” between the body’s internal clock and the demands of daily life.

Similar to traveling across time zones, this misalignment can lead to daytime sleepiness and reduced concentration. When chronic, social jet lag can lower work productivity and increase the risk of both physical and mental health problems. Previous studies have also linked social jet lag to obesity and weight gain.

When the decline in labor productivity was translated into economic terms, the researchers found that people with social jet lag lose an estimated ¥136,000 per person per year compared with those who get healthy sleep.

Assuming that individuals with social jet lag make up 16% of Japan’s population, the same proportion observed in the study, the total annual economic loss is estimated at roughly ¥1 trillion.

According to overseas research, productivity losses caused by sleep deprivation in Japan are estimated at about 3% of the country’s gross domestic product. Data published in 2024 by the OECD showed that people in Japan sleep an average of seven hours and 42 minutes per day, the shortest time among the 33 countries surveyed. This lack of sleep is believed to have a substantial negative impact on productivity.

The research group cautioned, however, that its findings should be interpreted carefully. They noted that the characteristics of the survey participants may differ from those of the average Japanese worker, and that labor productivity in the study was based on self-reported evaluations.

“By leveraging digital technologies to monitor individuals’ sleep and apply the insights to improve it, we may be able to achieve both better health for workers and higher labor productivity,” Yanagisawa said.

The group’s findings were published in a sister journal of the British scientific journal Nature.

Source: Japan Times
--Agencies